The present invention relates to a photopolymerizable mixture comprising a polymeric binder, an acrylate or alkacrylate of a polyhydric alcohol, and a photoinitiator or a photoinitiator combination, and to a corresponding recording material comprising a layer support and a photopolymerizable layer of the mixture.
Mixtures and materials of this type are used, for example, for producing printing plates and photoresists. The known mixtures are generally photosensitive in the near UV region; their photosensitivity is, however, substantially reduced by the addition of light-absorbing substances which are, for example, required for the production of intermediate masters or color proofing films.
The masters employed in reprography in most cases are based on silver halide materials which have the disadvantage of being very expensive. Therefore, photosensitive diazotype materials, which upon development give yellow or black azo dyes, are used for duplicating silver halide originals, such as microfilms. A diazotype material of this kind additionally containing a UV absorber has been disclosed in DE-B 1,286,897. Employing this process, only a limited image contrast can be achieved; moreover, films based on diazotype materials have a tendency to background discoloring.
DE-A 15 72 085 describes a photosensitive material for duplicating silver images, containing a photosensitive layer comprising o-quinonediazides and color pigments having an optical density above 1. The photosensitivity of this material, which absorbs in the same spectral region where it is photosensitive, is inadequate for practical use.
U.S. Pat. No. 3,218,167 discloses a photopolymerizable recording material, the photosensitive layer of which is strongly colored by the addition of a dye. The dye used is to absorb as little light as possible in the activating range of the photoinitiator. The material gives images exhibiting a good visual contrast, but these images are not suited as masters.
U.S. Pat. No. 3,353,955 relates to a similar photopolymerizable material that can be developed to give an image as a result of the different adhesion to the support film of the exposed and unexposed layer portions (peel-apart process). The material has a layer which is highly light-absorbing in the actinic spectral region. Due to the considerably reduced photosensitivity, only the upper portions of the photosensitive layer are completely polymerized, whereas the imagewise differentiation in the lower layer portions is low and insufficient for wash-out development. The peel-apart development gives images of relatively low resolution.
It is also known to obtain images of high light absorption from photopolymerizable materials by exploiting the different tackiness of exposed and unexposed areas and developing the exposed materials with a toner powder, optionally at elevated temperatures. The process is described in U.S. Pat. No(s). 3,060,024, 3,060,025 and 3,620,726. The images produced in this way are likewise resolved to a limited degree only.
Color proofing films are also produced and processed employing processes as described above. In most cases, a true rendering of the colors of the original can only be achieved by wash-out development, employing layers which are thoroughly dyed in the desired color. Here, too, at least the photosensitivity of colors absorbing in the shorter-wave region of the spectrum is considerably reduced.
German patent applications P 37 10 279.6, P 37 10 281.8 and P 37 10 282.6 disclose photo-polymerizable mixtures comprising polymeric binders, polymerizable acrylates or alkacrylates possessing photooxidizable groups, and photoinitiators or photoinitiator combinations, in particular photoreducible dyes and optionally certain photosensitive trichloromethyl compounds, as well as optional further free-radical-forming coinitiators. These mixtures are distinguished by a high photospeed, particularly in the longer-wave region of visible light, i.e., above 450 nm. The applications do not mention an addition of strongly light-absorbing substances, in particular UV absorbers, to the mixtures described therein.